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At least 19 recordsLinked to original sources
PubMed2026

Dissecting fluctuating selection: A unified population and quantitative genetics framework.

One of the longstanding debates in evolutionary biology is the effect of fluctuating selection on genetic changes in populations. However, the extent to which these periodic forces influence organisms at both genomic and phenotypic levels remains unclear. Despite the compelling evidence of fluctuating selection from recent studies, there is a disconnect between empirical and theoretical findings concerning the underlying mechanisms due to the limited evidence regarding the scale and processes that generate genome-wide oscillations. This study aims to elucidate how both genetic factors (e.g. heritability, number of causative loci) and ecological factors (e.g. season length, the difference in the phenotypic optima between seasons, population size dynamics) drive fluctuating selection and to identify the parameters that produce consistent oscillatory patterns. We developed a modeling framework integrating quantitative and population genetics to simulate a population under various selection regimes. We applied spectral analysis to detect periodicity, indicating cyclical selective environments. Our simulations highlight the conditions sustaining oscillations in allele frequencies over time. Spectral analysis successfully identifies the periodic patterns from allele frequency trajectories, even under highly complex selection regimes. Not only does our study clarify the conditions that yield oscillatory behaviors, but these parameters can also potentially be estimated in natural populations, providing a possibility of empirically testing these models.

Fluctuating selection↗
PubMed2026

Dissecting fluctuating selection: A unified population and quantitative genetics framework.

One of the longstanding debates in evolutionary biology is the effect of fluctuating selection on genetic changes in populations. However, the extent to which these periodic forces influence organisms at both genomic and phenotypic levels remains unclear. Despite the compelling evidence of fluctuating selection from recent studies, there is a disconnect between empirical and theoretical findings concerning the underlying mechanisms due to the limited evidence regarding the scale and processes that generate genome-wide oscillations. This study aims to elucidate how both genetic factors (e.g. heritability, number of causative loci) and ecological factors (e.g. season length, the difference in the phenotypic optima between seasons, population size dynamics) drive fluctuating selection and to identify the parameters that produce consistent oscillatory patterns. We developed a modeling framework integrating quantitative and population genetics to simulate a population under various selection regimes. We applied spectral analysis to detect periodicity, indicating cyclical selective environments. Our simulations highlight the conditions sustaining oscillations in allele frequencies over time. Spectral analysis successfully identifies the periodic patterns from allele frequency trajectories, even under highly complex selection regimes. Not only does our study clarify the conditions that yield oscillatory behaviors, but these parameters can also potentially be estimated in natural populations, providing a possibility of empirically testing these models.

Fluctuating selection↗
PubMed1975

Effect of temporal fluctuation of selection coefficient on gene frequency in a population.

The diffusion equations describing the change of gene frequencies are extended to indlude the effect of temporal fluctuation of selection coefficient that may persist for some generations. The equilibrium distribution of gene frequencies and the fixation probability of a mutant gene are obtained from the extended equations. Comparison is made with the experimental data on protein polymorphism. A possible bearing of the fluctuation of selection coefficient on the problem of molecular evolution is discussed in relation to the neutral theory.

Gene Frequency↗
PubMed2026

Seasonal fluctuations in fitness result in severe reductions in effective population size.

Genetic evidence for fluctuating selection has begun to accumulate for different species over the past few decades, especially for the Drosophila genus where studies have reported hundreds of loci undergoing putatively adaptive oscillations across successive seasons. However, most theoretical and simulation studies of fluctuating selection have relied on abstract or weakly parameterized models, making it difficult to assess their relevance for natural populations. In this study, we simulate multilocus seasonally fluctuating selection under a recently developed model and examine its effect on the variance effective population size (Ne ) at a genome-wide scale. By recapitulating genomic, demographic, and evolutionary parameters from natural Drosophila populations in our simulations, we were able to reproduce allele frequency oscillations reported in recent studies and show that these lead to ~50% genome-wide reductions in Ne . We also demonstrate that Ne reductions are well predicted by the maximum frequency amplitude among all adaptively fluctuating loci, and that the frequency amplitudes are largely determined by the number of adaptively fluctuating loci and the strength of their epistatic interactions. Our results demonstrate that fluctuating selection can substantially reduce effective population size and underscore the importance of temporally variable selection in shaping genome-wide patterns of variation beyond classical models.

Drosophila melanogaster↗
PubMed2026

Seasonal fluctuations in fitness result in severe reductions in effective population size.

Genetic evidence for fluctuating selection has begun to accumulate for different species over the past few decades, especially for the Drosophila genus where studies have reported hundreds of loci undergoing putatively adaptive oscillations across successive seasons. However, most theoretical and simulation studies of fluctuating selection have relied on abstract or weakly parameterized models, making it difficult to assess their relevance for natural populations. In this study, we simulate multilocus seasonally fluctuating selection acting on standing genetic variation under a recently developed model and examine its effect on the variance effective population size (Ne) at a genome-wide scale. By recapitulating genomic, demographic, and evolutionary parameters from natural Drosophila populations in our simulations, we were able to reproduce allele frequency oscillations reported in recent studies and show that these lead to ∼50% genome-wide reductions in Ne. We also demonstrate that Ne reductions are well predicted by the maximum frequency amplitude among all adaptively fluctuating loci, and that the frequency amplitudes are largely determined by the number of adaptively fluctuating loci and the strength of their epistatic interactions. Our results demonstrate that fluctuating selection can substantially reduce effective population size and underscore the importance of temporally variable selection in shaping genome-wide patterns of variation beyond classical models.

Drosophila melanogaster↗
PubMed1989

Rubidium and zinc fluctuations in selected tissues during the development of the BW7756 murine hepatoma.

In separate studies, radioisotopes 65Zn and 86Rb were used to monitor trace element fluctuations from normal in C57L/J mice throughout the progression of a murine hepatoma. Amounts too small to upset normal levels were injected directly into the blood stream. After an equilibration period, the whole mouse and various resected organs and tissues were counted. Compared to normal levels, rubidium in diseased mice was lower in kidney and blood, and elevated in skin and muscle. Diseased mice showed depressed levels of zinc in skin and muscle. Large fluctuations during different stages of tumor growth were observed for various other tissues and organs of diseased mice.

Animals↗
PubMed2025

Pervasive fitness trade-offs revealed by rapid adaptation to shifting population densities in large experimental populations of Drosophila melanogaster.

Trade-offs are an inherent feature of organismal biology that are expected play a fundamental role in the evolution of natural populations. Efforts to quantify trade-offs are largely confined to phenotypic measurements and the identification of negative genetic-correlations among fitness-relevant traits. Here, we use time-series genomic data collected during experimental evolution in large, genetically diverse populations of Drosophila melanogaster to directly measure the manifestation of trade-offs in response to fluctuating selection on ecological timescales. Specifically, we first conducted a lab-based selection experiment to quantify a genome-wide signal of antagonistic pleiotropy elicited in response to shifting population densities and associated with reproduction and stress tolerance selection. In doing so, we identified a putative role of two cosmopolitan inversions in these trade-offs. We then conducted an independent experiment to show that a simple manipulation of increasing population density under controlled lab-based conditions identified loci that are relevant to selection during population expansion and collapse in a complex, semi-natural setting. In concert, our results reveal how adaptation in complex, natural environments can be coarse-grained in such a manner to drive repeatable and predictable patterns of genomic variation, and further add credence to models positing a role of generic fitness trade-offs in the maintenance of variation in natural populations.

Drosophila melanogaster↗
PubMed1989

Longevity enhances selection of environmental sex determination.

Environmental sex determination (ESD) is a mechanism in which an individual develops as male or female largely in response to some environmental effect experienced early in life. Its forms range from sex determination by egg incubation temperature in reptiles to sex determination of photoperiod in amphipods. Previous theoretical work as suggested that ESD is favored by natural selection if the fitness consequences of the early environmental experience differ for males and females, so that an individual benefits by being male under some conditions and female under others. A drawback of ESD is that it enables climatic changes to influence the population sex ratio, and such fluctuations select against ESD. This study employed numerical analyses to investigate the balance between these two opposing forces. The negative impact of climatic fluctuations appears to depend greatly on species longevity: substantial between-year fluctuations are of little consequence in selecting against ESD in long-lived species because annual sex ratio fluctuations tend to cancel and thus alter the total population sex ratio only slightly. Thus, if a species is sufficiently long-lived, extreme ESD can be maintained despite only a weak advantage. This result offers one explanation for the failure to demonstrate an advantage for the extreme forms of ESD observed in reptiles.

Animals↗
PubMed1991

Sexual showiness and parasite load: correlations without parasite coevolutionary cycles.

Hamilton & Zuk (1982, Science 218, 384-387.) produced a model of sexual selection in which coevolutionary cycles of host and parasites generate consistently positive correlations between parent and offspring viability, and that animals choose mates for genetic disease resistance by scrutinizing characters whose full expression is dependent on health and vigour. They predicted a positive correlation between sexual showiness and parasite burden across species, and a negative correlation within a species. First, recent suggestions that interspecific correlations in the opposite direction to that indicated above are consistent with the mechanisms of Hamilton & Zuk's model are discussed. Second, it is shown that the model's predictions can be produced by heritable variation maintained by non-parasite fluctuating selection. In this case, the parasites associated with degree of sexual showiness are those able to amplify any initial heritable differences in vigour. Alternative sources of positive correlation between parent and offspring viability, which include the indirect effects of climatic change and exclude the need for host-parasite coevolutionary cycles, are also proposed.

Animals↗
PubMed1978

Isolation and characterization of mutants of human diploid fibroblasts resistant to diphtheria toxin.

Stable mutants highly resistant to the protein synthesis inhibitor diphtheria toxin (dipr) have been selected in human diploid fibroblast cells at a frequency of 1-8 X 10(-6). Treatment of cells with mutagens, (e.g., ethylmethanesulfonate, nitrosoguanidine, and ICR-170), increased the frequencies of dipr mutants by 50- to 500-fold in different experiments, and the optimal expression time for dipr mutation was about 5 days. All mutants examined thus far have bred true, and no effects of cell density or cross feeding have been observed on the selection. Fluctuation analysis showed that the dipr mutation occurs in these fibroblasts at the rate of 5-6 X 10(-7) mutations per cell per generation. Protein synthesis in mutant extracts was resistant to diphtheria toxin, indicating that the dipr lesion in such mutants lies in the protein synthesis machinery. The characteristics of the dipr marker should make this system particularly useful for studies of quantitative mutagenesis in human diploid cells.

Cell Line↗
PubMed1990

Hierarchical analysis of population genetic variation in mitochondrial and nuclear genes of Daphnia pulex.

The geographic structure of Daphnia pulex populations from the central United States is analyzed with respect to isozyme and mitochondrial DNA variation. The species complex consists of cyclic and obligate parthenogens. A hierarchical analysis of population structure in the cyclic parthenogens by using a fixation-index approach indicates that this is one of the most extremely subdivided species yet studied. This genetic structure, much of which accrues within 100 km, is certainly due in part to the limited dispersal ability of Daphnia. However, previous work has shown that fluctuating selection can account for the spatial heterogeneity in isozyme frequencies in these populations. This may explain why the population subdivision for the mitochondrial genome increases approximately three times as rapidly with distance as does that for nuclear genes, which is slower than the neutral expectation. The obligate parthenogens are shown to be polyphyletic in origin, evolutionarily young, and, in some cases, geographically widespread.

Animals↗
PubMed2025

The ecology and evolution of microbial immune systems: a look on the wild vibrio side.

Natural populations of vibrio beyond the well-studied pandemic strains of Vibrio cholerae, provide a powerful model for investigating the eco-evolutionary dynamics of microbial immune systems. Their genetic diversity, ecological versatility, ease of culturability and the availability of time-series data enable detailed studies of phage-host interactions in natural contexts. This review synthesizes recent advances in vibriophage research, highlighting key findings and emerging tools. High-throughput assays and genomic tools have offered new perspectives on phage specificity, host range and the evolutionary pressures shaping these interactions. Theoretical frameworks, such as arms race and fluctuating selection dynamics, are informed by empirical data from vibrio-phage systems, with time-series sampling providing crucial insights into their temporal and spatial dynamics. A major finding is the role of mobile genetic elements (MGEs) in encoding bacterial defence systems, which shape phage-host coevolution. Discoveries like the phage satellite PICMI illustrate how MGEs facilitate the transfer of antiviral systems, influencing ecological and evolutionary dynamics. The paradox of generalist vibriophages, rare despite their broad host ranges, is also explored. By integrating experimental approaches with field observations, vibriophage research advances microbial ecology and informs sustainable applications in aquaculture and phage therapy, reinforcing vibrios as a versatile model system.This article is part of the discussion meeting issue 'The ecology and evolution of bacterial immune systems'.

Bacteriophages↗
PubMed1990

Economics of human and canine rabies elimination: guidelines for programme orientation.

Analysis of the present situation in canine-rabies-infected countries shows that in most cases the levels of activities for controlling the disease in man and in dogs are far too low to prevent human deaths due to rabies and to eliminate the disease in the dog population. This article compares the two major orientations of a rabies control programme, i.e., prevention of the disease in man by intensifying and modernizing post-exposure treatment (strategy A) and canine rabies elimination by controlling the disease in the animal reservoir (strategy B). The operation of both strategies (A + B) together is also analysed. Based on the available data and assumptions for calculations of the costs, the results show that when the strategies are applied independently of each other, the annual cost of strategy B amounts to 25-56% of that of strategy A. When the two strategies are applied together, the actual annual spending related to the implementation of A + B becomes less than that of strategy A alone as from the fifth year following programme initiation. The sensitivity of the results was tested against selected fluctuations in the assumptions. An estimation of the costs of control activities per avoided death, according to the strategy applied, is also given. In countries where resources allocated to rabies control are inadequate in both the health and veterinary sectors, the comparison in costs and effectiveness of the two programme strategies for rabies elimination strongly suggests that consideration should be given to a national programme of dog rabies elimination. On the other hand, for obvious ethical reasons, if attention is paid to improvement of post-exposure treatment, then the national authorities should consider a planning horizon close to 15 years.

Animals↗
PubMed1985

The interaction of genetic drift and mutation with selection in a fluctuating environment.

The interaction of genetic drift, mutation, and selection in a random environment is investigated using an asymptotic analysis based on assumptions of weak mutation and strong selection. It is shown that genetic drift can be a potent force for removing variation from the population when the random environment tends to occasionally push alleles down to low frequencies.

Animals↗
PubMed1986

Directional selection and developmental stability: evidence from fluctuating asymmetry of dental characters in mice.

Developmental stability was assessed among lines of mice subjected to 11 generations of selection for increased (up line) and decreased (down line) widths of the first maxillary molar (M1), primarily to test the hypothesis that this stability would decline over time as a result of selection. Fluctuating asymmetry (FA) was used as an inverse measure of developmental stability, and was calculated for the M1 and a correlated character, the second mandibular molar (M2), in each generation. As measured by the regression of FA on generations, there was a statistically significant decline in stability only in the down selection line for the M2, and this trend did not differ significantly from that for the control line. The combined regressions obtained from pooling over all three lines were significantly different from zero in both molars, however, and this was taken to be evidence of a decline in stability due to increased homozygosity presumably generated by inbreeding during the selection experiment. The variation in FA among generations was greater for the selection lines than the control line for both molars, especially for the M2. The heritability of the M1 (and M2) was high, but there was no significant additive genetic variance for FA in either molar.

Analysis of Variance↗